The present invention relates to thermally, electrically and/or magnetically controllable lyotropic liquid crystal optical devices.
It more particularly applies in the display field, both as regards alphanumeric characters and more complex images, in the agricultural-food field for producing greenhouses, in the dwelling field for producing windows and in the field of bubble memories. The optical devices according to the invention can also be used for producing image converters, electrooptical or magnetooptical switches, spectacle lenses, or other variable transmission objects, etc.
The optical devices according to the invention can be used in all wavelengths from the infrared to the ultraviolet, whilst passing through the visible.
The liquid crystals are grouped into two main classes, namely thermotropic and lyotropic liquid crystals.
In thermotropic liquid crystals, the different crystalline phases are obtained by heating or cooling a given molecular compound (p-n-pentylcyanodiphenyl or p-azoxyanisole for example) or a mixture of compounds individually having liquid crystal properties. Examples of known thermotropic liquid crystals are nematics, smectics and cholesterics.
Lyotropic liquid crystals differ from thermotropic liquid crystals by the fact that they are constituted by a mixture of compounds not in themselves having liquid crystal properties.
Lyotropic liquid crystals are often constituted by a mixture of water and a surfactant. In such liquid crystals, the surfactant molecules are aggrevated and the aggregates organized to form a crystal lattice.
Known lyotropic liquid crystals are mesophases having lamellar, hexagonal, cubic and nematic structures. Often lyotropic liquid crystals contain more than 50% by weight of surfactants. In addition, their viscosity is often high, which makes their macroscopic orientation difficult.
The presently known lyotropic liquid crystals have never been used in optical devices, which is not the case with thermotropic liquid crystals.
The main reason is that they contain a large amount of water, that they have a high electrical conductivity and that the application of an electric field to these liquid crystals leads to an electrolysis of the water, whilst the electrical control is the most widely used in such devices.
The problem in thermotropic liquid crystals is of synthesizing molecules having a desired mesophase with a liquid crystal structure for the chosen operating temperature and which also have appropriate physical properties for the orientation of the molecules, such as a low viscosity.
Moreover, the presently used liquid crystals are formed by relatively expensive compounds giving a high price to the devices based on such liquid crystals.